<template>
  <div class="progress-bar" ref="progressBar" @click="progressClick">
    <div class="bar-inner">
      <div class="progress" ref="progress"></div>
      <div class="progress-btn-wrapper" 
        ref="progressBtn"
        @touchstart.prevent="progressTouchStart"
        @touchmove.prevent="progressTouchMove"
        @touchend="progressTouchEnd"
      >
        <div class="progress-btn"></div>
      </div>
    </div>
  </div>
</template>
<script>
import { prefixStyle } from "common/js/dom";
const transform = prefixStyle("transform");
const progressBtnWidth = 16;
export default {
  props: {
    percent: {
      type: Number,
      default: 0
    }
  },
  watch: {
    percent(newVal) {
      if (newVal >= 0 && !this.touch.initiated) {
        const barWidth = this.$refs.progressBar.clientWidth - progressBtnWidth;
        const offsetWidth = newVal * barWidth;
        this._offset(offsetWidth);
      }
    }
  },
  created() {
    this.touch = {};
  },
  methods: {
    // 进度条拖动效果
    progressTouchStart(e) {
      this.touch.initiated = true;
      this.touch.startX = e.touches[0].pageX;
      // 当前移动的位置
      this.touch.left = this.$refs.progress.clientWidth;
    },
    progressTouchMove(e) {
      if (!this.touch.initiated) return;
      const deltaX = e.touches[0].pageX - this.touch.startX;
      const offsetWidth = Math.min(
        Math.max(0, this.touch.left + deltaX),
        this.$refs.progressBar.clientWidth - progressBtnWidth
      );
      this._offset(offsetWidth);
    },
    progressTouchEnd() {
      this.touch.initiated = false;
      this._triggerPercent();
    },
    _offset(offsetWidth) {
      this.$refs.progress.style.width = `${offsetWidth}px`;
      // 按钮偏移
      this.$refs.progressBtn.style[
        transform
      ] = `translate3d(${offsetWidth}px, 0, 0)`;
    },
    _triggerPercent() {
      const barWidth = this.$refs.progressBar.clientWidth - progressBtnWidth;
      const percent = this.$refs.progress.clientWidth / barWidth;
      this.$emit("percentChange", percent);
    },
    progressClick(e) {
      const rect = this.$refs.progressBar.getBoundingClientRect();
      const offsetWidth = e.pageX - rect.left;
      this._offset(offsetWidth);
      this._triggerPercent();
    }
  }
};
</script>

<style scoped lang="stylus">
@import '~common/stylus/variable';

.progress-bar {
    height: 30px;

    .bar-inner {
        position: relative;
        top: 13px;
        height: 4px;
        background: rgba(0, 0, 0, 0.3);

        .progress {
            position: absolute;
            height: 100%;
            background: $color-theme;
        }

        .progress-btn-wrapper {
            position: absolute;
            left: -8px;
            top: -13px;
            width: 30px;
            height: 30px;

            .progress-btn {
                position: relative;
                top: 7px;
                left: 7px;
                box-sizing: border-box;
                width: 16px;
                height: 16px;
                border: 3px solid $color-text;
                border-radius: 50%;
                background: $color-theme;
            }
        }
    }
}
</style>